Pancreatic cancer continues to have one of the highest mortality rates of any malignancy and the 5-year survival rate remains less than 5% largely because of its propensity for metastasis and drug resistance. These problems have not yet been overcome, but recent research indicates that there is great variability in the intrinsic potential among distinct subpopulations of tumor cells to metastasize or resist treatment; that pancreatic cancer cells are functionally heterogeneous. We and others identified several phenotypically distinct pancreatic cancer cell populations that are enriched in tumor-initiating capacity, defining them as cancer stem cells (CSCs). The aldehyde dehydrogenase (ALDH)-expressing CSC population is associated with worse clinical outcomes, resistant to chemotherapy, and has higher metastatic potential. The mechanisms that regulate the functional characteristics of CSCs as well as what regulates the balance between pancreatic CSCs and non-CSCs are poorly understood. Our recent research indicates that pancreatic CSCs are maintained by direct interactions with certain proteins in the tumor microenvironment (TME) and focal adhesion kinase (FAK) signaling. We hypothesize that the TME plays a critical role in regulating the equilibrium between CSCs and non-CSCs, and that specific signaling pathways activated by the TME regulate CSC functional characteristics. Using our groups' expertise we propose to: 1) Determine the role of specific extracellular matrix proteins and integrins on FAK activation and regulation of the equilibrium between CSC and non-CSCs, 2) Evaluate the role of FAK activation on tumor progression and CSC function in the genetically engineered Ptf1a-Cre; KrasG12D/+; p53R172H/+ (KPC) pancreatic cancer mouse model, 3) Determine the most effective clinical setting in which antagonists of FAK can inhibit pancreatic cancer growth and metastasis using in vivo models, and 4) Evaluate if FAK protein expression can predict response to therapy. These studies will enhance our understanding of mechanistic interactions with the TME that regulate pancreatic CSCs, and will guide the clinical development of novel CSC-directed therapies.